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[34.02] Physical Properties of the Deep Impact Target Comet 9P/Tempel 1 from Spitzer and Hubble Space Telescope Observations

C.M. Lisse (UMD/JHU-APL), M.F. A'Hearn (UMD), M.J.S. Belton (Belton Space Initiatives, Inc.), Y.R. Fernandez (UH), O. Groussin (UMD), P. Lamy (Laboratoire d’Astronomie Spatiale), K.J. Meech (UH), I. Toth (Konkoly Observatory), H.A. Weaver (JHU-APL)

Comet 9P/Tempel 1 is the target of the Deep Impact mission to be launched at the end of this year. Accurate knowledge of the physical properties of the comet’s nucleus is important for mission success. Current published size estimates for the nucleus are uncertain by 50% [Fernandez et al. 2003] and the current best rotational solutions have periods of 22 and 42 hours [Belton and Meech, 2004].

In Spring 2004, with the comet outside the ice line and inactive and inbound on the final leg before the DI encounter, we obtained 12 spectrophotometric (7.5-40 microns) visits of the nucleus with the Spitzer Space Telescope over a 40 hour period in March 2004, and 18 photometric (F606) visits over a 42 hour period in May 2004 with the Hubble Space Telescope. Collating these observations into lightcurves, we have applied rotational and thermal models [Belton et al. 2005, Groussin et al. 2004] to derive values for the effective radius, axial ratio, pole position, bulk surface albedo, active surface area, and thermal inertia. Initial analysis of the observations has yielded a nucleus with an average radius of about 3 km, an axial ratio of about 3, a geometric albedo of about 4%, and an active surface fraction of about 8%. The thermal inertia is low, similar to that of other primitive bodies. The rotation pole orientation's J2000 RA and Dec are either (99^o,-19^o) or (60^o,+72^o) , with an error of about 4 degrees. We present the latest results of our observations and analysis here.

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The author(s) of this abstract have provided an email address for comments about the abstract: lisse@astro.umd.edu

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.